Internal combustion engine vehicles are by far the most common road vehicles in the world today. In addition to road vehicles, many other types of vehicles and equipment, such as cranes, bulldozers, electric generators, and so forth, are powered by internal combustion engines. Internal combustion engine vehicles offer undeniable advantages vehicles powered by other types of engines. Nonetheless, they suffer from undeniable disadvantages as well. Their exhaust is a major contributor to air pollution, particularly in densely-populated areas. The petroleum-based fuel they consume is unrenewable and, in time, supplies of petroleum will be depleted.
Alternatives to petroleum-consuming internal combustion engines have been proposed, and have been used in vehicles prior to the present invention. Renewable fuels, such as organic fuels derived from ethanol, are used as a supplement or alternative to gasoline in internal combustion engines. Although the energy output of such fuels is lower than gasoline, they burn more cleanly and do not produce oxides of nitrogen, which are a major component of automobile emissions. They are also renewable.
Electrically-powered vehicles have also been developed. Electric trains and trolleys, for example, have long been in use, and electric cars and trucks were produced and used many years ago. Electric vehicles are quiet and are very "clean" in that they produce no emissions at all. However, electric vehicles have a major drawback: they must at all times be connected to a source of electricity. This is not a problem for electric trains and trolleys, which are normally confined to a given route or right-of-way. An electrified overhead catenary is suspended above the tracks, and a pantograph (or current collector) on the vehicle makes contact with the catenary, connecting traction motors in the vehicle with the electrified catenary. For cars and trucks, however, which have no fixed route or right of way, this solution is impossible. As a result, electric cars and trucks rely on electric storage batteries to provide electricity to their traction motors.
Purely electric cars and trucks, however, are not ideal, either. The batteries tend to be heavy and bulky, adding weight to the vehicle and consuming space that might otherwise be used for passengers or cargo. Batteries also have a limited capacity, which limits the range of an electric vehicle. Batteries also need to be recharged, and over time will lose their ability to hold a charge. Batteries thus have a finite life, and must be replaced at the end of that life. Research has focused on reducing battery size and weight and on increasing battery life, but batteries are still a major problem, not the least of which is that fossil fuel must be burned in order to generate the electricity to charge the batteries in the first place. This leaves purely electric vehicles in the awkward position of contributing to air pollution while at the same time trying to avoid it.
Alternatives to batteries, such as solar panels, have been proposed to reduce dependence on batteries, but solar panels require abundant sunshine in order to be viable, and are not an option in many cases. Further research has focused on conversion of the direct current battery energy into DC pulse or AC schemes to power lighter, less expensive traction motors to compensate for some of the above drawbacks, but the conversion systems are complex and expensive.
Hybrid vehicles, which use energy from both electric batteries and an internal combustion engine, appear to offer a good compromise between purely electric vehicles and purely internal combustion vehicles. Hybrid vehicles tend to have smaller, lighter and less expensive batteries and a relatively long range than pure electric vehicles. They also tend to have relatively small (e.g., 30 hp) internal combustion engines, so they use less gasoline and emit fewer pollutants.
Prior to the present invention, in such vehicles the engine is operated at a constant speed for maximum efficiency. Propulsion of the vehicle is achieved by using an electric traction motor to power the drive wheels, while the internal combustion engine drives a generator to keep the batteries charged. By running the engine at a constant speed, fuel consumption and emissions are optimized. However, this approach demands the rapid draw of large amounts of current from the batteries during ignition and acceleration, which is inefficient because batteries work efficiently only when charged or discharged very slowly.
It has been proposed to use an alternative energy storage device to supplement the electrical output of a battery or a constant-speed internal combustion engine in a hybrid vehicle. U.S. Pat. No. 5,160,911, which is primarily directed to the structure of a toroidal superconducting magnetic energy storage unit, mentions that the disclosed storage unit can be used to augment the electrical output of a battery or a constant speed internal combustion engine in a hybrid vehicle. Energy stored in the storage unit can be used for acceleration, since neither a constant speed internal combustion engine nor a battery are able to provide the energy rapidly enough to adequately accelerate the vehicle. Thus, in the scheme briefly described in U.S. Pat. No. 5,160,911, the storage unit provides electrical output in addition to the output demanded from the battery during acceleration. Although U.S. Pat. No. 5,160,911 is silent on the point, presumably the storage unit only supplies electrical output after the maximum output of the battery has been reached. U.S. Pat. No. 5,160,911 also mentions that the storage unit can store energy recovered during regenerative braking of the vehicle, but does not explain how the energy is recovered or stored. Presumably, the storage unit is charged after the battery has been fully charged.
None of the prior attempts at designing a hybrid vehicle appear to have recognized, let alone addressed, the effect of their approaches on battery efficiency. For example, in the system suggested by U.S. Pat. No. 5,160,911, there is no disclosure of managing the energy draw from the battery, so that the battery presumably is rapidly discharged on acceleration and then rapidly charged during braking. Batteries do not operate most efficiently under such conditions.
The present invention improves battery efficiency, and therefore overall vehicle energy efficiency, by providing a superconducting magnetic energy storage device in conjunction with an energy management system in a hybrid vehicle to efficiently store and dispense energy. With the present invention, the state of a plurality of vehicle parameters, such as acceleration and braking, battery charge, and energy stored in the superconducting magnetic energy storage device, are sensed and used to control operation of the superconducting magnetic energy storage device. Depending on the state of the sensed parameters, the storage device is controlled to perform one or a combination of the following: 1) draw energy slowly from the battery, 2) slowly charge the battery, 3) supply burst energy to an electric machine to help drive the vehicle, and 4) store energy received from the electric machine during braking of the vehicle.
Most passenger cars do no require more than 20 hp for cruising at 55 mph. Greater power is needed only for acceleration and climbing hills. The present invention combines a small (and therefore lighter) internal combustion engine with an electric motor/generator and an energy storage device that recovers kinetic energy during vehicle braking and reuses it for acceleration and burst power. The present invention makes possible a highly energy-efficient, yet highly agile, hybrid vehicle.